Spindle motors are a commonly used in disk drives to simultaneously rotate each data storage disk being used by the disk drive. A stationary spindle or motor shaft of the spindle motor is anchored to the base plate of the disk drive. Each data storage disk is mounted on a rotatable hub of the spindle motor (e.g., using a disk clamp). The resulting combination will hereafter be referred to as a motor/disk assembly or as a disk pack. Multiple data storage disks would be mounted on the rotatable hub in vertically and equally spaced relation. One or more bearings are disposed between the spindle shaft and the rotatable hub that is disposed about the spindle shaft. Electromagnetic forces are used to rotate the hub about the stationary spindle at the desired velocity. Therefore, each data storage disk that is mounted on the hub also rotates about the stationary spindle shaft.
Concentric tracks are formed on each data storage disk used by the disk drive for storing information. The demand for increasing the data storage capacity of data storage disks has resulted in a corresponding increase in track density. Therefore, the read/write head(s) of the disk drive must be precisely positioned in order to avoid adversely affecting disk drive operations in some respect.
Another trend in the disk drive industry is increasing the rotational speed of the motor/disk assembly. Even a slight imbalance of the rotating motor/disk assembly may then generate rather significant forces that can adversely affect the ability to accurately position the read/write head(s) of the disk drive at the correct track of its corresponding data storage disk. Balancing of the motor/disk assembly is thereby commonly undertaken in the disk drive industry prior to shipping the drive to the customer. Single plane balancing of the motor/disk assembly that has been practiced in the disk drive industry commonly entails attaching one or more weights to one side of the motor/disk assembly. Not all imbalances may be alleviated to the desired degree by balancing within a single plane. Dual plane balancing of the motor/disk assembly has been practiced in the disk drive industry by attaching one or more weights at two different elevations corresponding with vertically spaced reference planes in an attempt to improve upon the potential inadequacies of a single plane balance. Notwithstanding the existence of dual plane balancing of the motor/disk assembly in the disk drive industry, there remains a need for improvement.